Aromatic compounds synthesized by the polyketide route are probably the most commonly occurring phenolic derivatives of natural origin, except the lignins. Little information is available on how microorganisms metabolize these compounds. Similarly, the catabolism of 2,3-dihydroxybenzoates, formed by the shikimate pathway, is poorly understood; as is the role 2,3-dihydroxybenzoates as general converging ring fission catabolites. We propose to: (a) establish the main types of catabolic routes used by microorganisms to degrade these compounds, (B) study in detail the oxygenases involved in these transformations, (C) establish the relationships, if any, of the enzymes (or metabolic sequences) involved, to the well described pathways of metabolism of other aromatic compounds, (D) provide further evidence for non-specific reaction sequences being responsible for the nutritional diversity of some microorganisms (E) study the possible evolutionary relationships of four enzymes sequential in a 2,3-dihydroxynenzoate metacleavage pathway, a decarboxylase, a hydrolase, a hydratase and an aldolase, (F) develop techniques for the direct selection of mutants defective in aromatic catabolic pathways; (G) understand the biochemical events that occur to allow mutant strains (acquisitive mutants) to grow with substrate analogs; and (H) to examine the basic genetic structure for the p-cymene and 4-methyl-o-phthalate catabolism by aerobic pseudomonads.